Printing paper containing low-strength, nonwoody lignocellulose and process of making the same



Dec. 19, 1961 FINE LY-DIVIDE D, NON-WOODY LIGNOCELLULOSE RETAINED ON SCREEN J. T. HENDERSON ETAL 3,013,935 PRINTING PAPER CONTAINING LOW-STRENGTH, NON-WOODY LIGNOCELLULOSE AND PROCESS OF MAKING THE SAME Filed March so, 1959 FIG; I

NON-WOODY LIGNOCELLULOSE, E.G. BAGASSE REDUCE MECHANICALLY IN AQUEOUS MEDIUM FlNELY-DIVIDED NON-WOODY LIGNOCELLULOSE OF 25-400cc C.S.F. FREENESS AND MULLEN BURSTING STRENGTH OF NOT OVER |O/ FORM A MIXTURE COMPRISING l5-85%OFABOVE FINELY- DIVIDED, NON-WOODY, LIGNOCELLULOSE AND 85-l5% OF A CHEMICAL LIGNOCELLULOSE PULP, DRY WEIGHT BASIS RUN INTO PAPER SMOOTH-SURFACED PRINTING PAPER OF HIGH OPACITY AND GOOD PRINTING QUALITIES FIG.2

(BOTH AT I00 cc c.s.F.)

GROUND BAGASSE PARTICLE SIZE (SCREEN MESH) JOHN T. HENDERSON SAMUEL B. KNAPP INVENTORS ATTY.

PRINTING PAPER CONTAINING LOW-STRENGTH,

NONWOODY LIGNGCELLULOSE AND PROC- ESS OF MAKING THE SAME John T. Henderson, Carnas, Wash., and Samuel B. Knapp, Kailua, ()ahu, Hawaii, assignors of one-half each to Hawaiian Development Company Ltd., Honolulu, Hawaii, a corporation of Hawaii, and Crown Zellerbaeh Corporation, San Francisco, Calif., a corporation of Nevada Filed Mar. 30, 1959, Ser. No. 802,775 19 Claims. (Cl. 162-142) The present invention relates to the manufacture of printing paper. It relates particularly to the manufacture of newsprint, book paper and other printing papers which contain a significant proportion of low strength, nonwoody lignocellulose, particularly bagasse.

Printing paper conventionally is made from mixtures of groundwood and chemical pulp. The groundwood supplies the required opacity, absorbency, bulk, smooth surface, the printability. The chemical pulp supplies the required strength.

As the availability of groundwood diminishes, it has become increasingly desirable to develop a substitute. Hence bagasse and other low cost, finely divided, nonwoody lignocellulose materials have been investigated.

Ellis, U.S. 1,344,625, and Vazquez, U.S. 1,688,904-5, and British 314,174 suggest producing a papermaking pulp by grinding bagasse or sugarcane, respectively. In

these procedures the grinding operation produces fibrous pulps having strength suficient for their conversion into newsprint without admixture with chemical pulps. However, the processes set forth in these patents have not assumed commercial significance.

We now have made the discovery that bagasse or other non-woody lignocellulose may be reduced mechanically to a finely divided product of negligible strength which, at any given freeness level, is much more finely divided than is groundwood.

If it were to be appraised by conventional standards developed for groundwood, such a product would be considered unsuitable for use in the manufacture of printing paper first because of its extremely low strength and second because of its high freeness. It would be expected from these characteristics that if the product were to be substituted for groundwood in the usual papermaking furnish, the resulting paper would be materially deficient I in strength, opacity, and surface smoothness.

Surprisingly, this is not the case. Newsprint in which it is incorporated instead of groundwood is at least as strong as conventional groundwood-containing newsprint. Because of the small size of its component particles, it has an exceptionally high surface to volume ratio and hence correspondingly high smoothing and opacitying qualities. Because of its high freeness, its drainage properties on the paper machine forming wire are far superior to those of groundwood.

As a result the chemical pulp, which is the other primary component of the papermaking furnish, may be beaten to a frecness level which is much lower than conventional. This develops greater strength in the final paper than is usually possible. Also, larger than normal proportions of chemical pulp can be added for the purpose of increasing strength without affecting adversely the printing qualities of the paper. Accordingly, we are able to employ a finely divided, non-woody lignocellulose that heretofore has been regarded as entirely unusable,

States Patent f 3,013,935 Patented Dec. 19, 1961 in the manufacture of groundwood-free printing paper of acceptable quality.

Considering the. foregoing in greater detail and with particular reference to the drawings wherein:

FIG. 1 is a flow plan of the herein described procedure; and

FIG. 2 is a plot of data obtained by screen fractionation of groundwood pulp and ground bagasse, illustrating the fundamental diiference in particle sizes at a given freeness level between these two materials.

Generally stated, the presently described invention comprises first mechanically reducing non-woody lignocellulose such as bagasse in aqueous medium to a finely divided product having a freeness of 25-400 cc. C.S.F. (Canadian standard freeness) and a Mullen bursting strength of not over 10%. From 15-85% of the resulting product then is mixed with from 85-15% of a chemical lignocellulose pulp, dry weight basis. The latter pulp may comprise a chemical bagasse pulp, if a printing paper composed entirely of that raw material is desired. After mixing the two components in the usual manner, the resulting pulp is run into paper, also in the usual manner.

The non-woody lignocellulose which may comprise the principal component of the herein described printing paper is derived from various plant materials such as whole or depithed bagasse, straws, grasses, cornstalks and the like. A preferred raw material comprises depithed sugarcane bagasse.

The non-woody lignocellulose may be employed without any chemical pretreatment whatsoever. It is reduced mechanically in any of the conventional refiners such as the single disc refiners, double disc refiners, rod mills, etc. Sufficient water is used to pass the lignocellulose through the refiner, which may be run at atmospheric pressure and at its normal operating temperature. If desired the reduction may be eifectuated under pressure, or at temperatures above those normally employed in the given refiner.

The resulting finely divided, non-woody lignocellulose has a consistency of from .l80%, preferably from 5-20%. Its freeness is between 25 and 400 00., preferably 40-250 cc. C.S.F. At freeness levels above 400 cc. the particle size becomes so great as to impair the opacifying power of the lignocellulose.

In general, the particles of the finely divided, nonwoody lignocellulose are much smaller for a given freeness level than are the particles of-groundwood pulp which it is designed to replace. In fact, they are more correctly described as having the characteristics of a powder than those of a fibrous product. As a result, the finely divided, non-woody lignocellulose has negligible bursting strength (less than 10% Mullen) and in most instances can not be used alone in forming a paper sheet. A sheet prepared from it even at the upper strength limit is scarcely self-sustaining; This is in sharp contrast to the groundwood used in the manufacture of conventional printing papers which must have a Mullen 3 prepared in the conventional manner has a particle size greater than 100 mesh.

As noted above, the herein described finely divided, non-woody lignocellulose has the ability to impart a higher degree of opacity and better printing qualities to the sheet than does conventional groundwood. Hence it may be combined to advantage with a chemical pulp of high strength in the production of a commercial printing paper.

Preliminary to such combination, the finely divided, non-woody lignocellulose may be screened and cleaned in the usual manner. Also, the chemical pulp may be beaten for improving its strength qualities. In view of the high freeness of the non-woody lignocellulose, the beating of the chemical pulp may be carried on until the pulp reaches a lower freeness level than usually is employed, thereby developing greater strength.

The finely divided, non-woody lignocellulose also may be bleached using sodium hydrosulfite, hydrogen peroxide, any of the various chlorine bleaches, or other agents conventionally used in the bleaching of papermaking pulps.

Chemical pulps which are mixed with the finely divided non-woody lignocellulose in the production of the herein described printing paper may be derived from either woody or non-Woody lignocellulose by any of the usual chemical pulping procedures including the kraft, soda, and sulfite pulping processes. It is a particular feature of the invention that it makes possible the production of an all bagasse printing paper, using ground bagasse and chemically derived bagasse pulps in combination with each other.

The relative proportions of finely divided non-woody lignocellulose and chemical pulp to be mixed with each other in producing the papermaking furnish are somewhat variable depending upon the sources of the raw materials and the qualities desired in the final paper.

In general, however, the papermaldng furnish comprises from -85% of finely divided, non-woody lignocellulose and 85-15% of the chemical lignocellulose pulp, dry weight basis. Suitable proportions of fillers, pigments, and other papermaking additives may, of course, be included in the furnish.

A preferred content of the furnish comprises from 30-70% of the finely divided, non-woody lignocellulose and from 70-30% of the chemical lignocellulose pulp. These proportions are also suitable for use when preparing an all-bagasse furnish.

When using a softwood sulfite pulp, as the chemical pulp, from 40-60% of the finely divided, non-woody lignocellulose and from 60-40% of the sulfite pulp may be used to advantage.

When a softwood kraft pulp is used as the chemical pulp, from 60-70% of the finely divided, non-woody lignocellulose and from 40-30% of the softwood kraft pulp may be used in view of the greater strength of the latter.

However, when using a hardwood kraft or soda pulp the preferred ranges would be from 35-45% of the finely divided, non-woody lignocellulose and from 65-55% of the hardwood chemical pulp because of the relatively low strength of the latter.

If desirable or necessary, the pulp mixture or its individual components may be cleaned, screened, beaten, bleached, or otherwise treated by the usual papermaking procedures for the development of desired properties. It then may be run into paper using conventional papermalting machinery operated under the customary conditions. The final product is eminently Well suited for use as newsprint, uncoated book paper, coated book paper and specialty printing papers. Its properties, as well as those of the fibrous materials from which it is manufactured, are indicated in the following examples.

4 EXAMPLE 1 This example illustrates a typical procedure for the preparation of the herein described finely divided, nonwoody lignocellulose.

Depithed bagasse was fed to a Sprout-Waldron single disc refiner at a consistency of 10% and with a plate clearance of inch. The partially ground bagasse then was passed five times through the refiner at a consistency of 5% while gradually reducing the plate clearance to zero. The freeness of the product was 300 cc. C.S.F. after the third pass, 150 cc. after the fourth pass, and 50 cc. after the sixth pass. Its Mullen bursting strength after the sixth pass was 2%.

EXAMPLE 2 This example illustrates the comparative particle size of the herein described finely divided, non-woody lignocellulose and the conventional groundwood pulp.

Ground bagasse, prepared in a manner similar to that described above, and conventional groundwood pulp prepared from softwoods were fractionated at various freeness levels in a Bauer-McNett fractionator equipped with U.S. sieve series screens. The results are given in Table I.

The surprisingly fine particle size of the ground bagasse, as compared to that of groundwood, is clearly evident from the above, at the cc. C.S.F. freeness level, the data being used in calculating the cumulative amounts of material retained on the screens, and plotted in FIG. 2.

EXAMPLE 3 The following example illustrates the bleachability of the presently described finely divided, non-woody lignocellulose.

Cleaned, ground bagasse pulps of 150 cc. C.S.F. freeness, prepared as in Example 1, were readily bleached under the conditions set forth in Table I1 and with the results set forth therein.

Table II Percent NazSrO; 1. 5 Percent Hi0: 2 Percent Sodium tripolyphos- Percent Nf12SiO (-i0 Be.) 5

p e Percent MgSOfliigO 0.5 pH at end of bleach. Percent NaOll. 2.0 Time, min Initial, pH 11 Temp, F Final pl'L. 8. 6 Consistency, perce 2. 5 Time, min 240 Initial brightness, percent Temp. F

G.E.R.S 42.0 Consistency, percent 8.0 Final brightness, percent Residual H202, percent... 58.2

G.E.R.S 62. 5 Initial brightness, percent .E.R.S .7 Final brightness EXAMPLE 4 This example illustrates the comparative freeness of pulp mixtures comprising kraft pulp-ground bagasse and kraft pulp-groundwood.

Ground bagasse, prepared as described in Example 1, and groundwood pulp were each mixed in varying proportions with a chemical kraft softwood pulp and the freeness of the resulting mixtures determined. The results are given in Table 111.

This example illustrates the production of an all bagasse printing paper.

Soda bagasse pulp at 400 cc. C.S.F. and ground bagasse at 50 cc. C.S.F., prepared as in Example 1, and bleached with hydrosulfite as in Example 3, were mixed in various proportions and made into paper. The test results are 6 pulp of 84% G.E.R.S. brightness beaten to 400 cc. C.S.F., and 40% of 50 cc. C.S.F, unbleached ground bagasse. The mixed furnish freeness was 320 cc. C.S.F.

Printing papers were prepared from both furnishes, the test results being given in Table VI.

Table VI Ground Ground 10 Bagasse Bagasse Douglas-Fir Cottonwood Kraft Kraft Bursting Strength. percent 42 31 Tearing Resistance, grams. 1. 59 0. 78 Breaking Length, meters 3, 830 3, 780 Caliper 1 1000" 5. 5.11

Opacity, percent 91 90 Brightness, percent G.E.R.S 51 57. 5

EXAMPLE 8 given in Table IV. a conventional U.S. newsprint containing 22% softwood Table IV Percent Percent Mixed Bursting Tearing Breaking Caliper, Opacity, Brightness, Soda Ground Freeness, Strength, Resistance, Length, 1/1000" Percent Percent Bagasse Bagasse cc. C.S.F. Percent grams Meters G.E.R.S.

EXAMPLE 6 sulfite pulp and 78% softwood groundwood. The other This example illustrates the preparation of a ground bagasse-hemlock sulfite printing paper.

C.S.F. hemlock sulfite pulp were made into paper, the

was an all bagasse newsprint prepared by the presently described process, e.g. that of Example 5. It contained 40% soda bagasse pulp and 60% ground bagasse.

The two samples were subjected to standard newsprint testing procedures. The results are presented in Table properties of which are given in Table V. V1 1.

Table V Percent Mixed Bursting Tearing Breaking Bright- Percent Ground Freeness, Strength, Resist- Length, Caliper, Opacity, ness, per- Snlfite Bagasse cc. C.S.F. percent auce, meters 1/1000 percent cent grams G.E.R.S

40 60 437 27. 1 103 2, 780 6. 4 86. 4 51. s 60 40 430 51. 7 114 4,660 5. 36 80.8 51. 4 so 20 7 408 80.0 117 7, 390 4 5 75.3 48.0

EXAMPLE 7 65 Table VII Conventional All Bagasse This example illustrates the preparation of ground us. News Newsprint bagasse-Douglas fir kraft and ground bagasse-cottonwood print kraft printing papers.

Two 21 ermakin furnishes were re ared. The first Basiswt.,lbs./ream 32 32 p p g P P 70 Bursting Strength, percent. 28 29 comprlsed 40% Douglas fir kraft pulp of 65% G.E.R.S. Caliper, 1/1000 35 346 Opacity 91. 4 92 brightness, beaten to 400 cc. C.S.F., and 60% of 50 cc. shemeld Smoothnesszl C.S.F. unbleached ground bagasse. The freeness of the wire 151 mixture was 333 cc. C.S.F. top 175 I The second furnish comprised 60% cottonwood kraft- 75 1 In inverse ratio to sheet smoothness.

It is readily apparent from the foregoing that by the present invention we have produced from bagasse or other non-woody lignocellulose a finely divided product which possesses remarkably high freeness and surprisingly small particle size, without subjecting the lignocellulose to any preliminary chemical treatment whatsoever. This product, when mixed with chemical pulps in varying proportions, then may be employed to advantage in the production of printing paper having a high degree of brightness, opacity, smoothness, bulk, ink receptivity, and other printing qualities. The characteristics of such papers, although devoid of groundwood, are at least equivalent, and in some respects superior, to those of conventional printing papers containing a mixture of groundwood and chemical pulp.

In addition, a low cost, commercially acceptable printing paper may be obtained solely from bagasse, using that waste raw material as a source of both the chemical and ground components of the papermaking furnish.

Having thus described our invention in preferred embodiments, we claim:

1. In the process of making printing paper, the step of preparing a furnish component therefor, which step comprises mechanically reducing non-woody lignocellulose in an aqueous medium to a finely divided, nonwoody lignocellulose product having a freeness of from 25-400 cc. CR8. and an inherent Mullen bursting strength of not over 10%.

2. The process of claim 1 wherein the non-woody lignocellulose comprises bagasse.

3. The process of claim 1 wherein the finely divided non-woody lignocellulose product has a freeness of from 40 to 250 cc. C.S.F.

4. The process of claim 1 wherein the non-woody lignocellulose comprises bagasse and wherein the finely divided, non-woody lignocellulose product has a treeness of from 40 to 250 cc. C.S.F.

5. In a printing paper furnish, the improved component comprising mechanically reduced, finely divided, non-woody lignocellulose having a freeness of from 25- 500 cc. C.S.F. and an inherent Mullen bursting strength of not over 10%.

6. The component of claim 5 wherein the non-woody lignocellulose comprises bagasse.

7. The component of claim 5 wherein the non-woody lignocellulose has a freeness of 40 to 250 cc. C.S.F.

8. The component of claim 5 wherein the non-woody lignocellulose comprises bagasse having a freeness of 40 to 250 cc. C.S.F.

9. The process of making printing paper which comsistency comprising 15-85% of the said product and 85- 15% of a chemical lignocellulose pulp, dry weight basis, and forming the mixture into paper.

10. The process of claim 9 wherein the non-woody lignocellulose comprises bagasse.

11. The process of claim 9 wherein the finely divided, non-woody lignocellulose product has a freeness of from 40 to 250 cc. C.S.F.

12. The process of claim 9 wherein the chemical lignocellulose pulp comprises a chemical bagasse pulp.

13. The process of claim 9 wherein the mixture comprises 3070% of the said finely divided, non-woody lignocellulose product and -30% of a chemical lignocellulose pulp, dry weight basis.

14. The process of claim 9 wherein the non-woody lignocellulose comprises mechanically reduced bagasse having a freeness of 40 to 250 cc. C.S.F. and the chemical lignocellulose pulp comprises chemical bagasse pulp.

15. A printing paper comprising a dried, felted mixture containing 15-85% finely divided non-woody lignocellulose having a freeness of 25-400 cc. C.S.F. and an inherent Mullen bursting strength of not over 10%, together with -15% of a chemical lignocellulose pulp, percent being expressed by weight, on a dry basis.

16. The printing paper of claim 15 wherein the non woody lignocellulose comprises bagasse.

17. The printing paper of claim 15 wherein the chemical lignocellulose pulp comprises chemical bagasse pulp.

18, The printing paper of claim 15 wherein the felted mixture contains from 30-70% non-woody lignocellulose and from 7030% chemical lignocellulose pulp.

19. A printing paper comprising a dried, felted mixture containing 30-70% finely divided bagasse having a freeness of from 40 to 250 cc. C.S.F. and an inherent Mullen bursting strength of not over 10% and from 70-30% of a Kraft bagasse pulp, dry weight basis.

References Cited in the file of this patent UNITED STATES PATENTS 1,623,184 Hinde Apr. 5, 1927 1,692,774 Grafflin Nov. 20, 1928 1,782,751 Vazquez Nov. 25, 1930 2.234,126 Mason Mar. 4, 1941 FOREIGN PATENTS 327,407 Great Britain Apr. 2, 1930 693,490 Great Britain July 1, 1953 828,036 Great Britain Feb. 10, 1960 OTHER REFERENCES Bhat: Bagasse Paper as Newsprint, from Indian Pulp and Paper, August 1953, pages 1-7.

USDA, Commercial Uses of Sugarcane Bagasse Studied, Nov. 9, 1955, page 1.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 o13 9s5- December 19 1961 John T. I'Iend,e1:son v et a1(,

It is hereby certified that error appears in the abor e nunibered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 7 line 41 v for "500" read 400 Signed and sealed this 8th. day of May 1962.,

-( SEAL) Attest: v I

ERNEST w. SWIDER DAVID DD v j V Commissioner of Patents I Attesting Officer 

15. A PRINTING PAPER COMPRISING A DRIED, FELTED MIXTURE CONTAINING 15-85% FINELY DIVIDED NON-WOODY LIGNOCELLULOSE HAVING A FREENESS OF 25-400 CC. C.S.F. AND AN INHERENT MULLEN BURSTING STRENGTH OF NOT OVER 10%, TO GETHER WITH 85-15% OF A CHEMICAL LIGNOCELLULOSE PULP, PERCENT BEING EXPRESSED BY WEIGHT, ON A DRY BASIS. 